The present invention relates to multiple reflector light or solar energy concentrators incorporating folded optics and systems using such concentrators. More particularly, the invention is concerned with an arrangement of optical elements for the efficient collection of light while minimizing complexities of optics needed to achieve light collection and concentration. At least three reflectors are involved. In a system, a receiver is placed in the focal zone of the third reflector. The present arrangement allows for the receiver to be in a fixed position, enhancing the ability of certain variants of the system to generate steam directly in the receiver. Preferred embodiments of the concentrator can be either in a trough or a dish configuration.
Solar concentrators are used in a variety of energy collection applications and can include large-scale uses that involve numerous unit systems spread over a wide area. Such systems are becoming more significant in view of growing power demands and particularly are of interest in third world countries where infrastructure and large land masses do not lend itself to construction of conventional power plants and distribution systems. However, the current solar concentrators suffer from certain insufficiencies. The mechanical elements and optical systems are complex, resulting in extremely high maintenance costs in electrical power generation and/or thermal based energy collection.
A recent example of a large-scale parabolic trough concentrator can be found in U.S. Pat. No. 5,460,163. A trough shaped mirror extends in a longitudinal direction. The reflector has a focal zone in which is placed a linear heat pipe receiver. The receiver is fixed in relation to the reflector, and thus, moves as the reflector tracks the sun""s diurnal movement.
Another linear reflector design is disclosed in U.S. Pat. No. 4,173,213. A series of split linear parabolic reflectors are used, an outer one is placed within the aperture of an inner one.
A parabolic dish concentrator is related in U.S. Pat. No. 5,882,434. A parabolic primary reflector has a flat region at the center of the dish forming an annular focal zone. A receiver in the form of a truncated cone is placed inverted such that the peripheral surface of the cone is in the annular focal zone. Photovoltaic cells are placed on the receiver""s peripheral surface.
A multiple primary reflector Fresnel system is disclosed in U.S. Pat. No. 5,899,199 to David Mills. An array of primary reflectors is arranged so as to reflect a large-scale linear target receiver.
A Cassegranian form of solar reflector is described in an article by Charles E. Mauk et alia, (Optical and Thermal Analysis of a Cassegrainian Solar Concentrator, Solar Energy Vol. 23, pp. 157-167, Pergamon Press Ltd. 1979). A hyperbolic reflector is placed in the focal zone of a parabolic dish primary reflector. The focus of the hyperbola is directed to the center of the primary parabola, where a furnace is placed to receive solar energy.
The present invention relates to multiple reflector solar energy concentrators and systems using such concentrators. More particularly, the invention is concerned with an arrangement of optical elements for the efficient collection of light while minimizing complexities of optics needed to achieve light collection and concentration. At least three reflectors are involved. A concave primary reflector receives the solar energy and sends it to a secondary convex reflector positioned in the focal zone of the first reflector. In turn, the secondary reflector sends the solar energy, at least in part, to a third non-imaging reflector positioned in the focal zone of the secondary reflector. In an energy collection system, a receiver is placed in the focal zone of the third reflector. The present arrangement allows for the receiver to be in a fixed position, enhancing the ability of certain variants of the system to generate steam directly in the receiver. Preferred embodiments of the concentrator can be either in a trough or a dish configuration.
The present invention has flexibility in the particular design of the reflectors. However, to maximize energy collection, the shape of each reflector affects the shape of the other reflectors. The primary reflector can vary from a circular arcuate shape to a parabolic shape. The change in shape will vary the position and size of the first focal zone. Thus, where the secondary reflector is placed in relation to the primary reflector and the precise shape of the secondary reflector, preferably a hyperbola, will vary as well. In turn, where the tertiary reflector is placed in relation to the secondary reflector and the precise shape of the tertiary reflector, preferably a compound parabola, will vary as well. In general, the tertiary reflector will be located adjacent to or in close proximity to the primary reflector, as shown in FIG. 1. To determine an optimal set of configurations, one can use conventional genetic algorithms to solve for the multiple solutions, as is known to those of skill in the art. Typically, one would select a set of reflector shapes that would reflect into the third focal zone at least 90% of the light energy falling within the aperture of the primary reflector.
In one broad embodiment, a solar energy trough concentrator comprises three reflectors. A primary reflector has a linear concave configuration that defines a first focal zone, and has a first longitudinal axis. A secondary reflector has a linear convex configuration that defines a second focal zone and has a second longitudinal axis in parallel alignment with the first longitudinal axis. The secondary reflector is disposed within the first focal zone. A tertiary reflector has a linear non-imaging configuration that defines a third focal zone and has a third longitudinal axis in parallel alignment with the first and second longitudinal axes. The tertiary reflector is disposed within the second focal zone. With this novel arrangement, light energy reflecting from the primary reflector is directed first to the secondary reflector, next to the tertiary reflector, and finally into the third focal zone.
In another broad embodiment, a solar energy dish concentrator comprises three reflectors as well. A primary reflector has a circular concave configuration that defines a first focal zone and has a first longitudinal axis. A secondary reflector has a circular convex configuration that defines a second focal zone. The secondary reflector is disposed within the first focal zone. A tertiary reflector has a circular non-imaging configuration that defines a third focal zone. The tertiary reflector is disposed within the second focal zone. With this novel arrangement, light energy reflecting from the primary reflector is directed first to the secondary reflector, next to the tertiary reflector, and finally into the third focal zone.
An object of the invention is to provide an improved solar collector system.
Another object of the invention is to provide a novel optical solar concentrator having a primary reflector with transducer decoupled from a secondary reflector.
A primary object of the invention is to permit an energy receiver to be placed in a final concentrating focal zone such that the receiver either does not have to move or moves only in a rotary fashion.
A further object of the invention is to provide an improved solar concentrator system having a tailored surface contour for both a primary and secondary reflector.
An additional object of the invention is to provide a novel solar collector device having a tailored parabolic primary reflector, a tailored hyperbolic secondary reflector, and a tailored non-imaging trough encompassing a receiver.
Still a further object of the invention is to provide an improved solar collector system having a secondary reflector system enabling selective transmission and reflection of light wavelengths to enable creation of photovoltaic power as well as collection and concentration of solar energy.
Yet another object of the invention is to provide a novel solar collector system having a solar transducer associated with the secondary reflector system enabling photoelectric energy to be produced for controlling and/or moving the solar collector system.
Other objects, advantages and variations of the invention will become apparent from the detailed description and drawings described hereinafter.